Polyurethane-urea elastomers have been widely used in industry for the manufacture of various moldings. The compounds are prepared from organic polyisocyanates and compounds having active hydrogen atoms capable of reacting with the isocyanate group. Compounds having active hydrogen atoms are organic compounds having molecular weights from 400 to about 12,000 and typically are polyols of the polyether or polyester polyol type. Many types of polyurethanes exist, and to differentiate these polyurethanes, they are often categorized by the process by which they are made as for example cast elastomers are formed by a casting process and RIM elastomers are formed by a technique called reaction injection molding. Foam elastomers, both rigid and flexible, are classified by their properties.
Reaction injection molding (RIM) is widely used today in the manufacture of molded parts particularly for the automotive industry. Examples of molded parts which can be produced by this process include automobile grilles and bumpers, support mountings for headlight and tailights, and in general, large moldings weighing from about 3 to 10 kilograms or more. A reaction injection molding involved mechanically mixing highly reactive starting components via multi-stream high velocity impingement and injecting the mixed component into the mold within a very short time by means of high output, high pressure dosing apparatus. Large quantities of liquid, highly reactive materials are delivered into the mold within a very short time and then cured, within a time usually from about 1 to 5 minutes.
RIM processes are shown in the following patents:
U.S. Pat. No. 4,218,543 discloses the RIM processing of methylene diphenylisocyanate-polyol systems which employ an aromatic diamine as a cross-linker or chain extender to provide rigidity for the urethane system. In the particular application described, diethyltoluenediamine, where the ethyl groups are ortho to each amino group, is used as the chain extender. As acknowledged in the patent, toluenediamine and many other aromatic diamines are either too reactive or are too slow in setting time for practical RIM systems.
U.S. Pat. No. 4,374,210 discloses a particular RIM process which utilizes a prepolymer as a reactive isocyanate material as opposed to the one shot process shown in the U.S. Pat. No. 4,218,543. Numerous polyisocyanate-prepolymers can be utilized in the RIM process; however, all are based upon 4,4'-methylene bis(phenylisocyanate) as the isocyanate. Aromatic diamines having alkyl group constitutents ortho to each amine group are used as the chain extender. An example of the aromatic diamines suited for the process was diethyltoluenediamine.
U.S. Pat. No. 4,048,105 shows the production of polyurethane-urea elastomers from an aromatic diisocyanate, polyol and aromatic diamine chain extender. The elastomer is formed by reacting a prepolymer of aromatic diisocyanate and alkane diol with a polyol blend containing long chain polyol.
U.S. Pat. No. 4,440,952 discloses the use of a monoisopropyl derivative of toluenediamine as a chain extender for polyurethane-urea systems where the isopropyl group is ortho to an amine group.
U.S. Pat. No. 4,487,908 discloses the production of reaction injected molded urethane elastomers from organic polyisocyanates, polyols and aromatic diamine chain extenders. Alkenyl succinic anhydrides are preferred as a class of additives to improve the green strength of the polymer.
There are numerous patents which show the use of various aromatic diamines in preparing polyurethane elastomers and foams and these include:
U.S. Pat. No. 3,752,790 which shows a chlorinated toluenediamine as an aromatic diamine for cross-linking urethane systems. The electronegativity of the chlorine atom deactivates the aromatic ring and tends to extend or delay the reaction rate. The chlorotoluenediamine derivative is suited for the production of large parts which require a formulation having a long "pot life".
U.S. Pat. No. 4,365,051 which dislcoses various aromatic amine esters, and nitriles as urethane cross-linkers. Examples include various alkyl diamino tertiary-butylbenzoates or diamino tertiary alkylbenzonitriles. In contrast to U.S. Pat. Nos. 4,218,543 and 4,374,210 the nitrile and benzoate groups are meta to the amine and not ortho to the amine group. The nitrile and ester groups deactivate the aromatic ring and thereby extend the pot life of the formulation.
U.S. Pat. No. 3,428,610 which discloses the production of cross-linked polyurethanes utilizing alkylated toluenediamine where the alkyl group is ortho to the amine. Numerous organic polyisocyanates and polyols are suggested as being suited for cross-linking by the alkyl aromatic toluenediamine chain extender.
U.S. Pat. No. 3,846,351 which discloses the utilization of secondary aromatic alkyl diamines as chain extenders and foam catalysts for polyurethane-urea elastomer forming compositions. N,N'-di-sec-butyl-p-phenylenediamine is one example of an amine having chain extending and catalytic activities.
European Pat. No. 0,069,286 discloses cellular polyurethanes which include alkyl-substituted phenylenediamines as chain extending agents. All diamines shown have an alkyl substituent in each ortho position to the amine.
U.S. Pat. No. 3,285,879 which discloses the utilization of N-mono-alkylaromatic diamines as chain extending agents for polyurethane-urea elastomers; and
U.S. Pat. No. 4,428,690, although nor prior art to this application, discloses a process for producing polyurethane-urea elastomers utilizing tertiary-butylbenzenediamine as a chain extender for the polyurethane-urea formulation. Tertiary-butylbenzenediamine was indicated as being a chain extender diamine which imparted longer "pot life" to a urethane formulation and a good tensile modulus to the resulting urethane-urea polymer.